The man suspected of killing a Colorado deputy and injuring three more appears to have exhibited warning signs before opening fire on a group of deputies Sunday morning in what law enforcement officials are calling an ambush.

As CrimeOnline previously reported, Matthew Riehl, 37, was identified as the gunman killed in a shootout in Highlands Ranch after he opened fire on five Douglas County Sheriff’s deputies, killing 29-year-old Deputy Zackari Parrish and injuring the remaining four responding officers, as well as two unidentified civilians.

The police officers were responding to a disturbance call for the second time on Sunday morning when Riehl opened fire while livestreaming the moments leading up to the shootout on Periscope. Both Riehl and his roommate, who has not yet been identified, reportedly called police in the early hours of Sunday morning.

In social media videos, Riehl identified himself as a combat veteran, and a National Guard spokesperson confirmed to KUSA-TV that he Riehl did served briefly in Iraq as part of the National Guard.

Social media posts in the weeks leading up the deadly ambush were critical of law enforcement, and Riehl’s meandering missives suggest the possibility of mental health issues. In a video that appears to have been uploaded not long before the deadly shootout, Riehl singles out a member of the Douglas County Sheriff Department, calling him a “pimp,” and claims that he will be running for sheriff himself, “on the Libertarian ticket.”

Students at University of Wyoming were warned in a November letter that Riehl, who graduated from the law school in 2010, had referenced the university in “rambling, nonsensical messages on his Facebook page,” CNN reports. According to the report, local and campus police were aware of the warning, and students were advised to call the police if they saw anyone matching Riehl’s description on campus.

According to the Los Angeles Times, law enforcement officials in Wyoming contacted police in Lone Tree, Colorado, to warn them about Riehl. But as University of Wyoming Police Chief Mike Samp told The Denver Post, authorities may not have been in a position to do anything about the potential threat.

“Wyoming statutes are pretty clear: If someone is not making an immediate threat, they cannot be held for a mental evaluation. They are very tough cases,” Samp told the newspaper.

Journalist JJ MacNabb, who reports on extremist and anti-government groups, was able to locate and save Facebook posts she believes were made by Riehl under the name Matt Gonzo before the page was taken down, and shared them on Twitter.